UC Davis UC Davis Previously Published Works Title Chemical and Sensory Characterization of Oxidative Changes in Roasted Almonds Undergoing Accelerated Shelf Life. Permalink https://escholarship.org/uc/item/61g6r83b Journal Journal of agricultural and food chemistry, 65(12) ISSN 0021-8561 Authors Franklin, Lillian M Chapman, Dawn M King, Ellena S et al. Publication Date 2017-03-21 DOI 10.1021/acs.jafc.6b05357 Peer reviewed eScholarship.org Powered by the California Digital Library University of California Article pubs.acs.org/JAFC Chemical and Sensory Characterization of Oxidative Changes in Roasted Almonds Undergoing Accelerated Shelf Life † ‡ ‡ † § Lillian M. Franklin, Dawn M. Chapman, Ellena S. King, Mallory Mau, Guangwei Huang, † and Alyson E. Mitchell*, † Department of Food Science and Technology, University of California, Davis, One Shields Avenue, Davis, California 95616, United States ‡ Covance Food Solutions, 365 North Canyons Parkway, Suite 101, Livermore, California 94551, United States § Almond Board of California, Suite 1500, 1150 Ninth Street, Modesto, California 95354, United States *S Supporting Information ABSTRACT: In almonds, there is no standard method for detecting oxidative changes and little data correlating consumer perception with chemical markers of rancidity. To address this, we measured peroxide values (PV), free fatty acid values (FFAs), conjugated dienes, tocopherols, headspace volatiles, and consumer hedonic response in light roasted (LR) and dark roasted (DR) almonds stored under conditions that promote rancidity development over 12 months. Results demonstrate that, although rancidity develops at different rates in LR and DR almonds, consumer liking was not significantly different between LR and DR almonds. Average hedonic ratings of almonds were found to fall below a designated acceptable score of 5 (“neither like nor dislike”) by 6 months of storage. This did not correspond with recommended industry rejection standard of PV < 5 mequiv peroxide/kg oil and FFA < 1.5% oleic. FFAs remain well below <1.5% oleic during storage, indicating that FFAs are not a good marker of rancidity in roasted almonds stored in low humidity environments. Regression of consumer liking to concentration of rancidity indicators revealed that selected headspace volatiles, including heptanal, octanal, nonanal, 2-octenal, 2-heptanone, 2- pentylfuran, hexanal, and pentanal, had a better correlation with liking than did nonvolatile indicators. KEYWORDS: almond, Prunus dulcis, HS-SPME GC/MS, peroxide value, hedonic analysis ■ INTRODUCTION triglycerides (i.e., oxidative rancidity).4,5 Both processes Sweet almonds (Prunus dulcis) are considered an excellent produce a range of primary lipid oxidation products (e.g., free source of dietary protein, fiber, and micronutrients such as fatty acids, lipid hydroperoxides, and conjugated dienes and vitamin E.1,2 Almonds are also high in unsaturated fatty acids trienes) and secondary lipid breakdown products (e.g., − aldehydes, ketones, alcohols, hydrocarbons, oxiranes, and (44 61% fat by weight) and low in moisture (less than 10% 4,12 moisture w/w) and are subject to lipid oxidation and the lactones). Primary oxidation assessment methods often − development of rancidity during storage.1 3 These changes can include measuring PV and conjugated dienes (CD). Peroxide − result in objectionable flavor and loss of nutritive quality.3 6 value measures the concentration of lipid peroxide, while CD assess the degree of double bond rearrangement co-occurring The two most abundant fatty acids in almonds are oleic acid 13 (18:1, 62−80%) and linoleic acid (18:2, 10−18%).1 Unshelled with the peroxidation of linoleic acid. Measuring FFAs in raw almonds have a shelf life of approximately 12 months due conjunction with lipid peroxidation indicates the degree of to relatively high concentrations of naturally occurring hydrolytic rancidity. PV is the most common method used by tocopherols (∼24 mg/100 g).7 Shelling and processing the industry to estimate oxidation in almonds, while methods such as FFA, CD, and tocopherol quantitation are less almonds exposes nutmeats to light, heat, moisture, and oxygen, 3,7,11,14,15 which can initiate lipid oxidation and shorten shelf life.5 commonly employed. Although lipid oxidation and the development of rancidity is a Because lipid hydroperoxides are themselves imperceptible to persistent problem for processors, there is no completely humans, measuring peroxidation may not directly correlate with fl 12 objective chemical method for determining the onset of avor changes in nuts. Quantitation of headspace volatiles rancidity. To date, the industry relies on indirect measures associated with rancidity (e.g., hexanal) has been used in many foods to better approximate development of rancid flavor and (i.e., peroxide value [PV] and free fatty acids [FFAs]) to 3,5,6,16,17 estimate lipid oxidation in almonds. Currently, there is no aroma. However, human perception of volatiles can ff uniform or standard method for detecting oxidative changes in di er based on unique product characteristics such as surface almonds and, more importantly, there is little data correlating area, moisture content, serving temperature, composition, and consumer perception with these chemical markers of rancid- − ity.3,8 11 Received: November 29, 2016 Rancidity development can occur through hydrothermal or Revised: March 6, 2017 enzymatic hydrolysis of triglycerides (i.e., hydrolytic rancidity) Accepted: March 11, 2017 and/or through the direct oxidation of fatty acids and Published: March 11, 2017 © XXXX American Chemical Society A DOI: 10.1021/acs.jafc.6b05357 J. Agric. Food Chem. XXXX, XXX, XXX−XXX Journal of Agricultural and Food Chemistry Article competing volatiles in the product headspace.18 Additionally, %), 1-H-pyrrole (98%), 1-octanol (99+%), butanoic acid (99+%), 3- sensory testing may not indicate whether the product is methylbutanoic acid (98+%), and nonanoic acid (99+%) were considered acceptable by the end-user, as trained sensory obtained from Sigma-Aldrich (St. Louis, MO, United States). judges should not answer affective questions.18 It is therefore Standards of hexanoic acid (98%), 1-butanol (99%), and ethyl 2- prudent to perform hedonic analysis of food products to (methylthio)-acetate (95%) were obtained from Acros Organics (Thermo Fisher Scientific Inc., Waltham, MA, United States). All benchmark chemical measures with changes in consumer 6 other standards, solvents, and reagents were purchased from either acceptance. Fisher Scientific Company (Fairlawn, NJ, United States) or Sigma- A number of studies have assessed consumer acceptance in Aldrich Chemical Co. These included the following: HPLC/ 3,9−11,15 relation to chemical measures of rancidity in almonds. spectrophotometric grade solvents ethanol, methanol, methyl tert- Most3,10,11,15 have focused on the effect of packaging type on butyl ether, glacial acetic acid, chloroform, and 2,2,4-trimethylpentane; consumer acceptance (and chemical markers of oxidation) analytical grade sodium hydroxide, hydrochloric acid (ACS certified during storage. For example, Mexis and Kontominas measured 36.5−38% w/w), potassium iodide (99.9%), and sodium thiosulfate (99%); and analytical standards of (±)-α-tocopherol, (+)-δ-tocopher- PV, hexanal, color, fatty acid methyl esters (FAME), and γ − consumer acceptance to study the effects of active packaging, ol, (+)- -tocopherol, volatile compounds (95 99%), and conjugated linoleic acid (99%). Exceptions included 2-(ethylthio)-ethanol (96%) nitrogen flushing, and packaging material on the oxidation of 3 (Alfa Aesar, Ward Hill, MA, United States) and 3-hydroxybutan-2-one whole, unpeeled raw almonds. Raisi et al. evaluated the impact (Supelco, Bellefonte, PA, United States). of packaging on PV, conjugated trienes, and hedonic ratings in Roasting and Storage of Samples. A 200 kg sample of dehulled, ground and whole unpeeled almonds for 10 months of storage raw, Nonpareil almond kernels with skin (from the 2014 harvest year) 15 under either vacuum, 95% CO2, or ambient atmosphere. was obtained from Blue Diamond Growers (Sacramento, CA, United Senesi et al. measured the effect of packaging on oxygen and States). Almonds were dry roasted in a BCO-E1 electric convection light permeability, storage atmosphere, and temperature on oven (Bakers Pride, Allen, TX, United States). Kernels were roasted under two different conditions: 115 ± 6 °C for 60 min and 152 ± 6 °C several aspects of oxidation and sensory quality of peeled whole “ ” “ ” raw almonds over 546 days of storage.11 Though a number of for 15 min to produce a light and dark degree of roast, respectively. studies have evaluated the relationship between packaging type, Almonds were divided into 480 g samples and placed in a controlled atmosphere chamber (KMF 240 Constant Climate Chamber by changes in oxidation indicators, and consumer acceptance, no Binder Inc. Bohemia, NY, United States). Samples were stored at 15 ± study directly compares oxidation indictors to each other in 1% relative humidity (RH) and 39 ± 1 °C for intervals of 1−12 their ability to correlate with consumer acceptance of almonds. months. Eight samples each of LR and DR almonds were randomly Additionally, there exists little published literature on the withdrawn from the chamber every month, mixed thoroughly, and volatile profile of roasted almonds during accelerated storage or repackaged into polyethylene vacuum sealed packages which were the relationship between volatile profile, rancidity indicators,